Conventional tennis balls are generally fabricated from a pair of hemispherical shells which are made of an elastomeric material and which are bonded with an elastomeric adhesive to one another along their edges to form a hollow spherical core. The hemispherical shells which constitute the core of the ball are formed by compression molding or injection molding. The core halves are placed in a mold and cured in the presence of heat and pressure to form a unitary hollow sphere containing a gas at a pressure of typically from ambient to about fifteen psi above normal atmospheric pressure.
The core is then covered with a pair of felt panels which have been cut from a suitable felt material generally in the shape of a dog bone. The unitary hollow sphere can be dipped in a panel adhesive and the felt panels attached thereto. The backside of the felt panels can also have panel adhesive applied thereto before they are applied to the unitary hollow ball. A different and curable seam adhesive is applied to the edges of the felt panels as by stacking a plurality of felt panels with their edges aligned, mechanically compressing the panels with their edges exposed and repeated dipping them into a bath containing the seam adhesive until a suitable build-up has been achieved. Once the seam adhesive edge coat felt panels are applied to a ball, they are cured. Thus, the panels and the seam adhesive become an integral part of the core.
In an effort to improve the visibility of the ball, in the past the manufacturers adopted dyed felt. Prior to the present invention, the state of the art was represented by an optic yellow felt ball in which the felt panels were attached together by a non-fluorescent off-white rubber adhesive seam adhesive. These seams are generally about 0.125 inches thick, 12.375 inches long, and have a width between about 0.05 and 0.15 inches (representing about eight percent of the total surface area.) Thus, to the extent that the pigment represents a visual advantage, a unpigmented seam represents a visual opportunity loss.